The present invention relates generally to air bags of the type utilized in vehicle occupant restraint systems.
Motor vehicles in service today are commonly equipped with air bag systems to supplement the protection provided by seatbelts. These air bag systems utilize at least one folded air bag in fluid communication with a source of inflation gas. A sensor is provided to detect a collision between the vehicle and another object. When such a collision is detected, the sensor actuates the source of inflation gas. As a result, the air bag is rapidly expanded to absorb at least a portion of the collision force that would otherwise have been imparted to the vehicle occupant.
Traditionally, a folded air bag is housed in the steering wheel and expanded when a collision is detected so as to protect the driver. A second air bag has been housed in the dash to protect an occupant located in the front passenger seat. In either case, it is important to design the air bag such that it will quickly deflate after it is inflated by the inflation gas. As a result, the air bag will collapse in a controlled manner as it is impacted by the vehicle occupant. Adequate support will thereby be provided to the vehicle occupant without excessive rebounding.
Due to various considerations, driver side air bags and passenger side air bags have often been constructed of different materials. For example, passenger side air bags have often been constructed of uncoated fabric. Driver side air bags, in contrast, have frequently been constructed of a base fabric woven from either nylon or polyester yarns, which have been coated with an appropriate elastomeric material to reduce permeability. Both passenger side and driver side air bags are often equipped with relatively large vent holes through which the inflation gas is expelled.
In addition to driver side and passenger side air bags, many vehicles are now being equipped with side cushions (or “side bags”), side curtains, or both. Side cushions are typically mounted in the outboard side of the seat, whereas side curtains are typically mounted along the roof rail of the vehicle. The side cushions are useful in protecting the middle and lower abdomen region of the occupant's body. Side curtains shield against breaking window glass and offer a degree of protection to the occupant's head.
In contrast to driver side and passenger side air bags, both side cushions and side curtains must remain inflated for relatively lengthy periods of time for continuous protection of the vehicle occupant. This is because the side of the vehicle is vulnerable upon impact to penetration of another vehicle or object. Thus, it is not unusual for vehicle manufacturers to require devices designed for side impact protection to remain inflated for several seconds.
The art has provided three primary techniques for the production of side curtains. The first such technique is to produce a one-piece side curtain using a jacquard loom. The one-piece curtain is coated with a suitable silicone or urethane to increase its air holding capability. A layer of nonwoven material is provided on the outside of the curtain nearest the door window to inhibit glass penetration. While these cushions have worked well for their intended purpose, jacquard looms are generally much more expensive than standard flat weaving equipment. In addition, it is relatively difficult to coat a one-piece curtain.
Second, the art has provided side curtains made from flat fabrics that have been coated with silicone. Pieces of the coated fabric are sewn together to yield a bag of the desired shape. One drawback of this approach is that the seams must generally be treated with a silicone spray or adhesive to plug the sew holes.
A third technique involves the production of side curtains using flat fabric coated with urethane. One advantage of urethane-coated fabric is that it can be welded to itself using RF technology or heat, thus eliminating the need to sew pieces of the coated fabric together. While a relatively thick coating of urethane is necessary in order to produce good welding, urethane-coated fabric is generally less costly than the use of a silicone-coated fabric which must be sewn.
It is desirable for the base fabric of a urethane-coated material to be made from a finer denier yarn in order to meet packaging requirements. This is because a urethane-coated material in which the base fabric is made from yarn of 630 denier (630d) or higher will often be too bulky for folding and packaging in the vehicle's roof rail. As such, fabrics made from yarns of smaller denier (such as 525d, 420d, 315d or 210d) are considered more desirable for side curtain applications.
One significant problem, however, has been noted with the use of base fabrics made from finer denier yarns. Specifically, the welded strength of the seam can exceed the strength of adhesion of the coating to the fabric. As such, the urethane coating may have a tendency to peel away from the base fabric. Better adhesion can be achieved with a looser weave, but a looser weave may adversely affect the strength characteristics of the resulting material. In addition, the urethane may simply bleed through the interstices of a loosely woven material during the coating process. Furthermore, even if successfully applied, the urethane coating may have a greater tendency to crack open if the base material is loosely woven.